The invention relates to a method for producing sheets from renewable raw materials in a continuous process which stands out against previously known methods through an essentially lesser energy demand.
In addition, the invention relates to a sheet which is produced with the method according to the invention.
Structural members made of renewable raw materials, especially for interior finishing work as well, are on increasing demand by wide consumer circles. Mostly, they have lower prices in contrast to structural members made of slowly growing natural raw materials. Compared with the artificial structural members, they are also preferred because they can be environment-friendly produced and provide a better atmosphere. In order to get the great demand under control manufacturing methods employing a continuous process are particularly suitable.
Conventional continuous processes—not only for producing sheets from renewable raw materials—provide that a mixture from that raw material and a binding agent are processed into a sheet using pressure and/or temperature.
Sheets from renewable raw materials and methods for producing thereof are then known. In the publication DE 28 41 172 A1, there is disclosed a multi-purpose sheet which is made of vegetable materials of agricultural source and/or wood material as well as of another additives. For the production, the above mentioned ingredients provided with binding agents are integrated into a sheet fill and are further processed into a sheet using pressure and temperature. Cement, gypsum or comparable materials are used as binding agents.
In the publication DE 198 10 862 C2, there is also disclosed a method by means of which insulating boards can be produced from renewable raw materials—in this case being of very finely sliced and spliced open straw—using the supply of pressure and temperature. The treatment of material is very cost-intensive. Both above mentioned methods additionally require pressure as well as heating up in order to cause the sheets produced therewith to reach a condition in which they can be further processed. With the last mentioned insulating board it is even necessary to additionally carry out a precompaction. Applying the raw materials with pressure is very expensive because of the application of great presses which have to be operated and maintained. Also, supplying of heat involves high amount of energy.
In the publication DE 19811807 A1, there is presented the production of an insulating member by means of which, in the intermittent process the individual components are mixed with each other, and then this mixture is added into moulds and is pressed, respectively, and in the continuous process the mixture is added into a belt-type press or plate-type press and is shaped under pressure. Even though a reduction of the high amount of energy is already achieved by this type of production without any influence of temperature, applying pressure requires operation of a machine and thereby increases expense for energy. This is disadvantageous.
In the publication DE 198 29 261 A1, there is disclosed a method according to which renewable raw materials such as e.g. straw or grass are subjected to shredding and are then mixed with a binding agent. This mixture is afterwards deposited upon a conveyor belt having a side limit stop and, as necessary, is processed into the final product under light pressure and through a thermal treatment. With this invention, heat is used to solidify the mixture consisting of renewable raw materials and binding agents to a sheet. For the production of this sheet also high energy consumptions to operate such devices required for the thermal treatment are to be taken into account as well.
From the German Offenlegungsschrift DE 1 0 2007 026 638 A1, there is known a sheet having heat resistance which is produced from renewable raw materials. In this sheet the renewable raw materials are mixed with a binding agent consisting of magnesium carbonate, magnesium oxide, magnesium chloride and water, and are constrained to harden in moulds. Disadvantages of this sheet are that it is comparatively heavy and not capable of being produced in an endless process.